Refining and recrystallizing of sugars using aqueous alcohols



United States Patent Oifice 3,454,425 Patented July 8, 1969 3,454,425REFINING AND RECRYSTALLIZING OF SUGARS USING AQUEOUS ALCOHOLS BruceSmythe, 47 Gritfith Ave., Roseville, New South Wales, Australia, andRobert Staker, 26 Millwood Ave., Chatswood, New South Wales, AustraliaNo Drawing. Continuation-impart of application Ser. No. 208,171, June15, 1962. This application Oct. 10, 1966, Ser. No. 585,322

Int. Cl. C13f N US. Cl. 127-64 2 Claims ABSTRACT OF THE DISCLOSURE Amethod of producing refined sugars from a sugar consisting of crystalsbearing a film of molasses, wherein the sugar bearing molasses is washedat certain temperatures in a first solvent that contains appreciablequantities of dissolved sucrose until the molasses film is substantiallyremoved from the crystals and subsequently dissolving the clean crystalsin a second selective solvent at a temperature between 70 and 150degrees C. so as to dissolve the crystals, cooling the hot liquor tocrystalize the sucrose and subsequently separating the refinedcrystalized sugar from the mother liquor.

The present invention is a continuation-in-part of United States Patentapplication Ser. No. 208,171, filed June 15, 1962.

The invention relates to the refining and recrystallizing of sugars.More particularly, it relates to the removal from raw sugar of colourfactors and various other impurities, and to the preparation therefromof a refined sugar in crystalline or liquid form.

The different varieties of raw sugar (e.g. mill white, cane raws, beetraws) all consist of crystals of sucrose surrounded by a viscous film ofmolasses. For a given raw sugar, the ratio of total impurities to totalsucrose may be 1:99, but the ratio of impurities occluded in thecrystals to impurities in the molasses film may be 1:9.

Since most of the non-sucrose components of raw sugar are contained inthe external molasses film, it is standard practice to perform apreliminary afiination by washing the molasses film from the crystals.The separated crystals are then further purified by a procedure (I)terminating in the production of refined sugar, while the molasses rawwashings are treated by a procedure (II) terminating in the productionof additional raw sugar and the final rejection of a very impure wastemolasses.

According to a known method currently favoured, the washing fluid usedfor the preliminary affination of raw sugar is hot aqueous syrup, e.g.impure recycled raw washings. When this is mixed with raw sugar, a magmais obtained comprising sucrose crystals dispersed in a stable colloidalsuspension of (essentially) diluted molasses. The greater part of thisdiluted molasses is then removed from the crystals by centrifugation.

By procedure (I), the separated crystalline material coated withresidual molasses-is mixed with hot water to give an aqueous sucrosesolution containing dissolved or colloidally suspended impurities notremoved in the preliminary affination step. This solution is thentreated with selected materials (e.g. lime, carbon dioxide,superphosphate, sulphur dioxide, bone char, activated charcoal, orselected combinations thereof) to elfect the removal of certainimpurities; and sucrose is recovered from the purified syrup by stepsincluding evaporation, crystallization and centrifugation. If required,sucrose of still higher purity may be obtained by redissolving therecovered sucrose and repeating the last-mentioned steps.

By procedure (II), the raw washings material is submitted to chemicaland/or physico-chemical treatment, and a low-grade sugar is recoveredfrom the treated washings. This sugar is used to augment the supply ofraw sugar to the preliminary affination stage, and a Waste molassesliquor is finally rejected containing approximately equal parts byweight of impurities and sucrose.

This known method suffers from many disadvantages of which the moreobvious ones are noted below.

(1) The preliminary affination of raw sugar with hot aqueous syrupresults not only in the dilution of the molasses film but also in thedissolution of a certain fraction of the crystalline sucrose. Since itis considerably more difficult to recover refined sugar from the rawwashings than from the crystalline sucrose, this dissolution process canonly occur at the expense of refining efficiency. While the dissolutionof sucrose can be greatly reduced by further increasing the sucrosecontent of the washing syrup toward saturation level, the viscosity ofsuch a syrup is so high that (i) the entire atfination process becomestediously slow, and (ii) the efficiency of raw washings separation bycentrifugation becomes much reduced. In practice, a compromise is soughtbetween these opposing factors.

(2) In many crystal manufacturing processes it has been foundeconomically desirable to employ a continuous crystallizer of the typeincorporating a first region for crystal growth and a second region fromwhere crystals of desired size may be recovered by gravitysettling.However, by virtue of the high viscosity of aqueous sugar solutionsgenerally and by virtue of the small density differential between suchsolutions and crystalline sucrose, it has not been found commerciallypracticable to employ such continuous crystallizers for the purpose ofrecovering crystallized sucrose from mother liquor in the terminal stepsof procedure (I). For this reason, the recovery of crystallized sucrosefrom mother liquor has hitherto been performed by employing aninherently less eflicient batch process (involving sugarboiling), thesuccess of which is determined in part by operator skill.

Additionally, the high viscosity of sugar solutions impedes theseparation of recrystallized sucrose during centrifugation. This problemis particularly pronounced when the recrystallized material consists ofcrystals of small size (e.g. 0.1 mm. diameter).

(3) The waste molasses liquor finally rejected in the terminal steps ofprocedure (II) is an aqueous mixture containing an unsatisfactorily highratio of sucrose to impurities (as noted previously, about 1:1 byweight).

It is an object of the present invention to select solvents andconditions for their use which overcome (inter alia) the abovedisadvantages in the refining and recrystallizing of sugars.

It is a particular object of the invention to select a versatile solventin which,

(i) 'by the selection of appropriate conditions, untoward dissolution ofcrystalline sucrose does not occur during the preliminary aflination of,raw sugar, but in which,

(ii) by the selection of appropriate different conditions, washed rawsugar can be readily dissolved to give a solution of such low densityand viscosity that sucrose can be recrystrallized and separatedtherefrom in a com mercially attractive process employing a continuouscrystallizer of the described known type.

We have ascertained by experiment that many of the components of rawsugar which are substantially soluble in concentrated aqueous sucrosesolutions, are substantially insoluble-or at least controllablysolubleeither in selected organic solvents or in selected aqueousmixtures containing such organic solvents.

The selectivity of a solvent for any given component of a mixture refershereinafter to the ratio of the weight dissolved of that component tothe weight dissolved of the remaining components when a quantity of themixture is added to a quantity of the solvent.

The solvent selectivity of water for the components of raw sugar isrelatively poor: firstly, because many of the components (sucrose andimpurities alike) are inherently soluble in water; secondly, becauseother components-even if not inherently soluble in water per se aresoluble, or form stable colloidal suspensions, in aqueous solutionscontaining sucrose. On the other hand, the solvent selectivity of someorganic liquids for the sucrose component of raw sugar is conspicuouslygreater than that of water; further, many of the raw sugar impuritiesare not only inherently insoluble in such organic liquids per se, butare also substantially insoluble in their sucrose-containing solutions.

We have now found that this high solvent selectivity is alsocharacteristic of some binary solutions consisting of water in admixturewith an organic solvent selected from those organic solvents having asolvent selectivity for sucrose in raw sugar greater than that of water.

The criteria by which suitable organic solvents can be selected forincorporation in these sucrose-selective binary solutions are:

(i) the organic solvent must be freely miscible with water at allconcentrations to give a single phase binary solution, and

(ii) dissolution of sucrose in the resulting binary solution must notresult in the separation therefrom of a second phase.

Thus, on the basis of the first criterion, sucroseselective combinationsof water and n-butanol must be rejected as unsuitable since theycomprise a single phase binary solution only at very low or very highconcentrations of one component. Again, on the basis of the secondcriterion, sucrose-selective combinations of water and i-propanol mustbe rejected as unsuitable sincewhile they comprise a single phase binarysolution at all concentrations-separation of a second liquid phaseoccurs when a significant quantity of sucrose is dissolved therein. Onthe other hand, sucrose-selective combinations of water and certainother alcohols (e.g. methanol, ethanol, furfuryl alcohol), orcombinations of water and certain substituted alcohols (eg.Z-methoxy-ethanol, 2- ethoxy ethanol), satisfy both these criteria.Combinations of water and alcohols (or substituted alchools) whichsatisfy all the criteria are hereinafter referred to as aqueousalcohols.

By manipulating variables of concentration and temperature, we havediscovered that aqueous alcohol combinations may be selected for use inthe refining and recrystallizing of sugars by methods which overcome thedisadvantages of the prior art.

When hot aqueous alcohol syrup is substituted for hot aqueous syrup as awashing agent in the preliminary aflination of raw sugar, comparativetests with different aqueous alcohol combinations indicate that arelative increase in the alcohol content of the combination isassociated with the following effects:

(a) a relative reduction in the dissolution of crystalline sucrose;

(b) a relative increase in the quantity of precipitated impurity;

(c) a relative improvement in the ease of separating precipitatedimpurity by centrifugation;

(d) a relative reduction in the raw washings viscosity;

(e) a more unfavourable distribution of colour factors between thoseremaining in the washed crystals and those removed by the raw washings.

These effects are, of course, not independent of each other. Thus, theeffects (b) and (d) are at least partly determined by the low sucroseconcentration in the washing solution, this being directly attributableto effect (a). Effect (c) is related to the fact that organic insolublesare increasingly less hydratedhence, less bulky-in aqueous alcohols ofincreasing alcohol content.

When hot aqueous alcohol is substituted for hot water as a solvent forwashed raw sugar in purification procedure (I), comparative tests withdifferent aqueous alcohol combinations indicate that a relative increasein the alcohol content of the combination is associated with effectssimilar in kind to those noted under (b), (c), (d) and (e), and isadditionally associated with:

(f) a relative increase in the density differential betweenrecrystallized sucrose and supersaturated mother liquor.

When an aqueous alcohol syrup washing agent is used for the preliminaryaffination of raw sugar, or when an aqueous alcohol solvent is used forthe dissolution and recrystallization of sugar, comparative testsindicate that a relative increase in the temperature of the operation isassociated with the following effects:

(g) a relative increase in the dissolution rate of crystalline sucrose;

(h) a relative increase in the absolute solubility of sucrose;

(i) a relative increase in the rate of crystallization of sucrose fromsupersaturated solution;

(j) a relative increase in the rate of inversion of sucrose to reducingsugars;

(k) a relative reduction in the quantity of precipitated impurity.

pendent increase in the concentration of dissolved sucrose.

Having regard to the above trends, we have been able to define optimumconditions for using selected aqueous alcohol combinations in therefining and recrystallizing of sugars; and we have established that, bythe use of these conditions, the noted disadvantages of the prior artcan be overcome and considerable economies can be effected.

The invention provides a method of producing refined sugar from a sugarconsisting of sucrose crystals bearing a film of molasses, said methodincluding the steps: washing the sugar at a temperature of between about20 and 40 C. in a selected solvent until the molasses film issubstantially removed from the crystals, and separating the cleanedcrystals from the washings; said solvent containing sucrose dissolved ina combination consisting of 15-40% by weight of water and -60% by weightof a selected alcohol; said alcohol having a solvent selectivity forsucrose in raw sugar greater than that of water, and being selected fromthe group consisting of those alcohols and substituted alcohols whichare freely miscible with water at all concentrations to give a singlephase binary solution from which a second liquid phase is not separatedby the dissolution therein of sucrose.

It has been noted previously that the dissolution of crystalline sucroseby hot aqueous syrup can be greatly reduced by further increasing thesucrose content of the washing syrup towards saturation level, but thatsuch syrups must be avoided because of their high viscosity.

This viscosity restriction does not apply when aqueous alcohol syrup isused for washing purposes, and the dissolution of crystalline sucrose(for which aqueous alcohols are highly selective solvents) may thereforebe very effectively inhibited by ensuring that the aqueous alcohol syrupis nearly sucrose-saturated. As will be illustrated in subsequentexamples, very satisfactory aqueous alcohol washing syrups can be madeby mixing a quantity of raw sugar with the selected aqueous alcoholcombination.

Aqueous alcohols usable according to the invention consist of 15-40% byweight of water and 85-60% by weight of alcohol, preferred combinationsfor particular Reducing sugar, Ash,

percent percent Colour 1 1 Colour units by transmittanoy of a standardsolution using light of wavelength 420 millimicron my.

2 Unwashed raw sugar.

3 Sugar washed with aqueous syrup (refinery conditions).

4 Not estimated.

Very poor.

Poor.

We have found that no significant advantage is to be gained by washingraw sugar with aqueous alcohols at temperatures above 40 C.;accordingly, since it is always preferred to operate at substantiallyambient temperatures, we have limited ourselves in the above statementof the invention to washing Within the temperature range 20-40 C.

The ratio by weight by solvent to raw sugar is not critical, butpreferred values lie between 04:1 and 1:1. In practice, the upper limitis set by economic factors while the lower limit is set by the need toform an easily worked slurry.

In performing this aspect of the invention sugar crystals are mixed withthe solvent until the film of surface molasses is substantially removed.The period required for this condition to be achieved is short and iseasily determined by observation. We have found generally that washingfor a minute is as effective as washing for an hour.

The molasses washings (containing insoluble and precipitated impurities)are separated from the crystals by methods known per se, e.g. involvingcentrifugation. If desired, crystal quality can be upgraded at thisstage by rinsing the crystals, e.g. during centrifugation, with a freshquantity of the selected solvent. It will be appreciated that water ordilute non-alcoholic aqueous syrups cannot be used satisfactorily forrinsing in this manner, since they are proved to efiect excessivedissolution of crystalline sucrose; however, aqueous alcohols or aqueousalcoholic syrups are not subject to this disadvantage and can be usedfor rinsing with great success.

The separated molasses washings are treated (e.g. by steps includingadditional centrifugation or by filtration) to recover a solvent fromwhich suspended impurities have been removed. This solvent may of coursebe recycled or used again in some other suitable stage of the refiningprocess.

A method has been described previously (D. F. Othmer and A. H. Luley:Sugar 43,7,26) wherein raw sugar is washed with anhydrous alcohols (e.g.methanol) for the purpose of avoiding excessive dissolution ofcrystalline sucrose; and it has also been known according to thispreviously described method to use such alcohols at high temperatures(e.g. the boiling point of methanol, 64.7 C.) for the purpose ofsoftening the molasses film. We have shown, however, that the use ofanhydrous conditions is undesirable, since it leads to a precipitationof sucrose from the molasses film adhering to crystals of raw sugar(such precipitated sucrose passes intothe molasses washings from whichit cannot be easily recovered). Furthermore, as noted above, we haveestablished that washing can be conducted satisfactorily at temperaturesnot in excess of 40 C.

The following examples illustrate the preliminary afii nation of rawsugar by washing with aqueous alcohol solvents according to the methodof the invention. The yields are consistent with a crystalline sucrosedissolution of between about 2.56%.

EXAMPLE I An aqueous ethanol washing syrup was made by dissolving 101 g.of a cane raw sugar with a mixture of 195 mls. water and 574 mls.ethanol (i.e. an aqueous ethanol containing 70% ethanol by weight). Thissolution was then mixed with 2,000 g. of a raw sugar at 25 C. for oneminute. Washed sugar crystals were recovered from the slurry bycentrifugation and the insoluble residue was filtered out of the rawwashings. Analyses of the raw sugar, washed sugar and insoluble residueare given below.

Raw sugar: Percent Reducing sugar 0.39 Ash 0.24

Yield (a) washed sugar, 1,933 g.:

Reducing sugar 0.03 Ash 0.09 Yield (b) insolubles, 1.2 g. ash 35 EXAMPLEII A sample of beet raw sugar was treated as in Example I. Analyses ofthe raw sugar, washed sugar and insoluble residue are given below.

Raw sugar: Percent Reducing sugar 0.008 Ash 0.62

Yield (a) Washed sugar:

Reducing sugar 0.004 Ash 0.08 Sucrose recovery 94 Yield (b) Insolubles:Substantially no insolubles.

EXAMPLE III An aqueous ethanol washing syrup was made by dissolving 75g. of a cane raw sugar in a mixture of 150 g. water and 350 g. ethanol(i.e. an aqueous ethanol containing 70% ethanol by weight). Thissolution was then mixed with 1,060 g. of the raw sugar at 22 C. for oneminute. Washed sugar crystals were recovered from the slurry bycentrifugation and the insoluble residue was filtered out of the rawwashings. Analyses of the raw sugar, washed sugar and insoluble residueare given below.

Raw sugar: Percent Reducing sugar 0.51 Ash 0.46

Yield (a) Washed sugar, 1005.5 g.:

Reducing sugar 0.06 Ash 0.15 Yield (b) Insolubles: 1.06 g. ash 35 Theinvention also provides an alternative or ancillary method of producingdefined sugar from a sugar consisting of sucrose crystals bearing a filmof molasses, said method including the steps: dissolving the sugar in aselected solvent at a temperature of between about 70 and 150 C. under apressure suflicient to prevent boiling, and separating insolubleimpurities from the hot liquor; said solvent consisting of 15-40% byweight of water and -60% by weight of a selected alcohol; said alcoholhaving a solvent selectivity for sucrose in raw sugar greater than thatof water, and being selected from the group consisting of those alcoholsand substituted alcohols which are freely miscible with water at allconcentrations to give a single phase binary solution from which asecond liquid phase is not separated by the dissolution therein ofsucrose.

Depending on the desired quality of the product, the sugar materialprocessed by the above methods of dissolution may be a crude raw sugar(bearing a viscous film of highly impure molasses) or a raw sugar thathas already been washed (bearing a diluted film of molasses). Sugar ofhighest refined quality cannot of course be recovered from crude rawsugars by applying merely the dissolution method of the invention;nevertheless, such products-even if somewhat inferiorare useful for manypurposes.

When raw sugars are refined by a two-stage process involving bothwashing and dissolution according to the invention, it is preferred toemploy the same aqueous alcohol combination in both stages of theprocess. Alcohol to water ratios preferred for dissolution are the sameas those already noted for washing, viz, in the concentration range7565% by weight in the case of unsubstituted alcohols and in theconcentration range 85-75% by weight in the case of substitutedalcohols.

Loss of alcohol by evaporation is at least minimised according to theinvention by ensuring that dissolution is carried out under non-boilingconditions. If this cannot be achieved under atmospheric pressure at theselected dissolution temperature, higher pressures are imposed. Theabsolute solubility of sucrose in aqueous alcohols rises sharply withincreased temperature, hence it is preferred to employ temperatures asnear to the defined upper limit as practicable. However, selectedtemperatures usually do not exceed 120 C., since otherwise adversecolour formation and undue inversion may occur. Dissolution may often beperformed at temperatures higher than 120 C., if the period of retentionat these temperatures is suitably short. The required time period fordissolution may of course be reduced by carrying out the process on asugar that has been ground to a small particle size.

At any given temperature, the ratio of Weight of sol vent to raw sugarrequired for dissolution is of course determined only by solubilityconsideration.

It will be appreciated that the refined sugar produced by the abovedissolution method may be recovered, as desired, in liquid orcrystalline form. A liquid sugar may be obtained from the purified hotliquor by steps including distillation to remove the alcohol content;alternatively, a crystalline sugar may be obtained from the hot liquorby steps including cooling, crystallization and separation of sugarcrystals from the resulting magma. The hot sugar solutions may betreated with a discolourising agent (eg. activated charcoal) prior torecovering the product in either of these forms.

When forming a solid product, the hot liquor is preferably cooled bycounter-current heat exchange and is then allowed to crystallize. Acontrolled degree of cooling ensures a steady rate of crystal growth andan even-sized product. As is well known, the average crystal size of theproduct may also be controlled by deliberately seeding the solution witha selected quantity of small crystals.

The supersaturated mother liquor has a low viscosity and the crystallineproduct can be readily separated from it by centrifugation orfiltration.

The crystallization step may be split into two or more stages in series,so that no stage operates under such a large temperature reduction thatfalse grain becomes troublesome or heat exchange surfaces become fouledby crystal growth.

The separated crystals may be dried without further treatment;alternatively, they may be redissolved in a further quantity of aqueousalcohol and a more refined product can then be obtained byrecrystallization.

The crystals are dried preferably by means of a hot air stream, andprovision is made for alcohol recovery from the hot air stream.Alternatively, a vacuum drying technique may be employed. The driedcrystals when cool are ready for packing.

The mother liquor separated from the crystallized sugar can be furthertreated to recover additional sucrose (e.g. by cooling to sub-ambienttemperature or by diluting with extra alcohol). Alternatively, it may beused as an aqueous alcohol syrup in the described Washing process of theinvention.

The alcohol may be recovered from the exhausted mother liquor bystripping in a distillation column, and the reclaimed alcohol isretained for re-use. If sufliciently pure, the aqueous syrup remainingafter distillation may be used as a basis for liquid sugar manufactured;if not sufiiciently pure, it may be further exhausted of its su crosecontent by conventional recrystallization techniques or may be discardedas conventional molasses having an impurities to sucrose ratio of 1:1.

The following two examples illustrate the purification of raw sugar bysteps including dissolution in hot aqueous alcohol solvents according tothe method of the invention.

EXAMPLE IV Solution was made by dissolving 250 g. of a Washed cane sugarat 99 C. in a mixture of g. of water and 320 g. of Z-methoxy-ethanol(i.e. an aqueous 2-methoxy-ethanol containing 80% by weight of thealcohol). After centrifuging to remove insoluble matter, the solutionwas reheated; 10 g. of 48/ 65 sugar was added for seeding purposes andthe mixture was allowed to crystallize by cooling slowly, with stirring,to 25 C. The product was recovered by centrifugation.

Yield (a) Product sugar, 195 g.:

Size of crystals, diameter mm 0.5 Reducing sugar percent 0.004 Ash do0.006 Yield (b) Insolubles 0.30 g.:

Ash do 35 EXAMPLE V A solution was made by dissolving 260 g. of a washedbeet raw sugar at 70 C. in a mixture of 120 g. of water and 280 g. ofethanol (i.e. an aqueous ethanol containing 70% by weight of ethanol).The solution was filtered to remove precipitated impurities, small seedsugar crystals were added and the mixture was allowed to crystallize bycooling slowly, with stirring to 30 C.

Yield (a) Product sugar, 17 g.

Size of crystals, diameter mm 0.5 Reducing sugar percent 0.002 Ash do0.005

Yield (b) Insolubles, negligible.

The invention additionally provides a method of recrystallizing a sugarconsisting of substantially pure sucrose crystals, said method includingthe steps: dissolving the sugar in a selected solvent at a temperatureof between about 70 C. and 150 C. under a pressure sufficient to preventboiling, cooling the liquor to recrystallize the sucrose, and separatingsugar crystals from the liquor; said solvent consisting of 1540% byweight of Water and -60% by weight of a selected alcohol; said alcoholhaving a solvent selectivity for sucrose in raw sugar great er than thatof water, and being selected from the group consisting of those alcoholsand substituted alcohols which are freely miscible with water at allconcentrations to give a single phase binary solution from which asecond liquid phase is not separated by the dissolution therein ofsucrose.

The following example illustrates the application of this aspect of theinvention to obtain a sucrose product of fine particle size.

EXAMPLE VI A solution was made by dissolving 1,200 g. of refined whitesugar at C. .(40 p.s.i.g.) in a solvent consisting of 700 g. ethanol and300 g. Water (i.e. an aqueous alcohol containing 70% alcohol). A fondantslurry was added to seed the mixture as it was cooling to 40 C. Theproduct was recovered by filtration.

Product sugar yield, 940 g.

Size of crystals mm. diameter 0.1

Insoluble sludge materials resulting from the practice of the inventionmay be treated with hot aqueous alcohol solvent to recover the freesucrose occluded therein. Residual sludge materials after solventremoval (e.g. by distillation) are found on analysis to have animpurities to sucrose ratio of between :1 and 1. Such materials arediscarded.

The final insoluble fraction comprises organic materials and mineralmatter in the proportions roughly 2:1, the organic materials portionbeing a potential source of such materials as higher saccharides,proteins, waxes, etc.

The herein described process of refining and recrystallizing sugars bymeans of selected aqueous alcohols may be applied (independently or incombination) to yield products having greater purity and/or smallercrystal size than was hitherto feasible using the non-alcoholic solventsand methods known to the prior art. The invention has enabled closercontrol in the process of dissolution and recrystallization (continuouscrystal separation now being possible) and all manufacturing costsbothcapital and operating-can be reduced.

We claim:

' 1. A method of producing refined sugar from a sugar consisting ofsucrose crystals bearing a film of molasses, said method including thesteps: washing the sugar at a temperature of between about 20 and 40 C.in a first selected solvent comprised of water and an alcohol selectedfrom the group consisting of methanol, ethanol, furfuryl alcohol,Z-methoxy-ethanol, and Z-ethoxy-etha- 1101, until the molasses film issubstantially removed from the crystals, separating the cleaned crystalsfrom the washings, dissolving the cleaned crystals in a second selectedsolvent comprised of water and an alcohol se lected from the groupconsisting of methanol, ethanol, furfuryl alcohol, Z-methoxy-ethanol,and 2-ethoxy-etha- 1101, at a temperature of between about 70 and 150 C.under a pressure sufficient to prevent boiling, separating insolubleimpurities from the hot liquor, cooling the hot liquor to crystallizethe sucrose, separating the refined crystallized sugar from the motherliquor and drying the separated crystals; said first selected solventbeing substantially saturated with sucrose dissolved in a combinationconsisting of 15-40% by Weight of water and 85- -60% by weight theselected alcohol; said alcohol having a solvent selectivity for surcrosein raw sugar greater than that of water, and being selected from thegroup consisting of those alcohols and substituted alcohols which arefreely miscible with water at all concentrations to give a single phasebinary solution from which a second liquid phase is not separated by thedissolution therein of sucrose.

2. A method of producing refined sugar according to claim 1 in which thesolvent used to wash the crystals is recycled mother liquor from thecrystallization step.

References Cited 824,929 12/ 1951 Germany.

MORRIS O. WOLK, Primary Examiner.

DAVID G. CONLIN, Assistant Examiner.

US. Cl. X.R. 12758, 63

